Historically, nearly 220 million acres of sagebrush steppe existed in North America, making it one of the most widespread habitats in the continent. Sagebrush ecosystems are found throughout western North America providing diverse habitats for a variety of flora and fauna. Numerous species of the sagebrush steppe are sagebrush obligates and thus, are dependent on the sagebrush biome for their survival. Exemplary sagebrush dependent species include Sage Grouse (Centrocercus urophasianus), Brewer's Sparrow (Spizella breweri), Sage Thrasher (Oreoscoptes montanus), Sage Sparrow (Amphispiza belli), Pygmy Rabbit (Brachylagus idahoensis), Sagebrush Lizard (Sceloporus graciosus), Sagebrush Vole (Lemmiscus cirtatus), Pronghorn Antelope (Antilocapra americana) to name a few.
Unfortunately, human activity and invasion by non-native plant species has resulted in the loss of over half of the sagebrush ecosystem. The threats to the ecosystem continue to this day. Indeed, of the remaining 100 million acres of sagebrush steppe habitat in the Intermountain West, over half are infested by invasive grasses such as e.g., downy brome (Bromus tectorum L., aka cheatgrass). Invasive grass weeds are adapted to a wide range of annual precipitation, soil conditions and disturbance thus, there is little in the natural ecosystem to contain their spread.
Invasive grass weeds also exert negative impacts on croplands and agriculture. At least 15 million acres of cropland in the west are infested with some level of downy brome. The mat-like rooting system of downy brome and its ability to grow further into the winter season than wheat, allows downy brome to easily outcompete wheat. Indeed, downy brome is very competitive with winter wheat for soil water and nutrients. Fifty downy brome plants ft−2 can remove available soil water to a depth of about two feet. Thus, a moderate infestation of two to 10 plants ft−2 reduces wheat yields 30-50%. A heavy infestation can reduce yields by 80%. Although herbicides are available, most are expensive, vary in effectiveness, and do not reduce the seed bank. Seed bank longevity is typically underestimated and some downy brome seeds can remain in the soil for years.
In addition to competing for water resources, downy brome produces significant amounts of dead, above-ground biomass that accelerates wildfire in both rangeland and in cropland. The dead, above-ground biomass comprises a fine, dense mat of highly flammable fuel susceptible to ignition, which accelerates fire cycles. Accordingly, fire size, intensity, and frequency have increased dramatically with the expansion of annual grass weed infestations. In addition to disrupting the ecology and ecosystem, fire can be devastating to rangeland and standing crops, and leaves the soil more vulnerable to erosion and runoff.
Unfortunately, while many approaches have been taken to control invasive grass weeds, so far, none have had widespread success.
Thus, what is needed in the art are compositions and methods that permit control of invasive grass weeds without negatively affecting native plants or crops, and not changing the soil ecosystem, thereby allowing for preservation and restoration of sagebrush-steppe habitats and increased agricultural productivity. Fortunately, as will be clear from the following disclosure, the present invention provides for these and other needs.